This invention relates to a composite hydraulic cylinder apparatus associated with a pneumatic cylinder and an oil hydraulic cylinder.
When movable elements of various types are mechanically actuated, a moving control system with a pneumatic cylinder mechanism or an oil hydraulic cylinder mechanism is generally employed, the cylinder mechanisms are also used as buffer means when the movable elements are stopped, and these mechanisms have merits and demerits as discussed hereinafter.
Since air is a pressure medium in the case of a moving control system with the pneumatic cylinder mechanism, the entire apparatus which contains primarily of an air cylinder and a switching valve together with a control system can be inexpensively constructed, but since the pressure medium is compressible fluid, the responsiveness of the mechanism when the movable element is stopped is often erroneous and has low reliability.
To eliminate the drawbacks, a mechanical brake means is provided via a piston rod. The piston rod moves during a period of the braking state in the case of stopping at an intermediate stroke position of the brake means so that the movable element overruns the target stopping position, and the positioning accuracy of the movable element is erroneous.
In addition, the abovementioned mechanical brake means generally has other drawbacks such as small holding force, low reliability, wear of the brake due to repeated use for a long term to cause the braking characteristic to be deteriorated.
Since the pressure medium (oil) is noncompressible fluid in case of the movable element control system with the oil hydraulic cylinder mechanism and the movement of the piston immediately stops when high pressure oil supply into the cylinder is stopped, the positioning performance is good, and larger output and holding force can be provided by the noncompressive pressure medium, but since the oil hydraulic unit is ordinarily expensive and large sized, it is difficult to satisfy the inexpensive facility cost and space-saving requirements.
As a new proposal to eliminate the drawbacks of the abovementioned cylinder mechanisms, there is a combination of two sets of cylinder units associated by disposing in tandem or parallel to drive a movable element partly by a pneumatic pressure and to brake the element partly by an oil hydraulic pressure, thereby controlling to position the movable element by a stop valve provided in the oil passage of the oil hydraulic system.
Since such a proposed example moves the movable element by a pneumatic system, and stops the element by an oil hydraulic system, the apparatus can be inexpensive as compared with the case that the entire system is composed of an oil hydraulic system, the positioning accuracy of the movable element can be enhanced by the oil hydraulic control, and the example enhances the economy and the operability since the stop valve of the oil passage of the oil hydraulic system is provided as the control of the movable element and may be merely opened or closed.
Since a plurality of independent cylinder units are disposed in tandem or parallel and associated in the proposed example, the longitudinal or lateral size is increased by the plural cylinder units, and this example could be improved in the compact construction and size.
Further, there is no interchangeability in the buffer means when the movable element is stopped.